The two of us don't agree on everything, and we have found ourselves sometimes on different sides of the debate about how best to transition to clean electricity in New England. But we do agree on this: it's time to focus on clean and affordable transportation.

Over the past decade, Massachusetts' electric sector has made steady progress towards a clean energy economy. Now it's time for the Bay State to take on the largest source of pollution in the state: transportation. That's why New England's power generators are joining together with scientists and environmental advocates to call for new programs to address pollution from transportation.

Massachusetts has developed some of the strongest policies in the country to reduce pollution from electricity. Massachusetts leadership helped establish first-in-the-nation market-based limits on power plant emissions, the Regional Greenhouse Gas Initiative (or "RGGI"), which not only limits pollution from power plants but also has enabled us to invest millions in energy efficiency and renewable energy. These investments have helped make our economy the most energy-efficient in the country.

These and other complementary policies have helped achieve dramatic reductions in carbon dioxide emissions from power plants. Overall, electric sector emissions are down nearly 60 percent compared to 1990 levels.

Unfortunately, thus far we have not been able to make the same degree of progress in other areas of our economy. Transportation has been particularly challenging. Pollution from our cars and trucks, rather than our power plants, is now the largest source of emissions in Massachusetts. It's also the one area where emissions are about the same today than they were in 1990, as increases in total driving outpace gains in fuel efficiency.

The good news is, the lessons learned from the progress in electricity de-carbonization can be applied to transportation. In particular, taking the model of RGGI to establish a market-based, regional emissions program can help Massachusetts continue to lead the way in reducing emissions while continuing to grow the economy.

One reason to now focus on transportation is we have the technology to significantly reduce pollution that simply didn't exist when RGGI was created more than a decade ago. Electric vehicles are now available in nearly all makes and models, from passenger cars to SUVs and buses and trucks. These cars are fun to drive, cheap to maintain and to fuel, and thanks to the progress our electric sector has made, EV's produce just a small fraction of the emissions of a conventional vehicle. When connected to the New England grid, electric cars get the emissions equivalent of a 100 mpg internal combustion car, a car that does not exist in the marketplace.

Massachusetts has set an overall goal of putting 300,000 electric vehicles on the road by 2025. But currently we only have about 12,000 electric vehicles in the state. By creating a market-based system to address the critical emissions from transportation we can help bring electric vehicles and other new investments in clean transportation into the mainstream. As part of that we are committed to working together with policymakers, the electricity grid operator, consumer groups and other stakeholders to address how to integrate this changing industry into the electricity market as well as developing the infrastructure necessary to make these vehicles as convenient as any other car.

These investments will require us to identify new sources of funding for clean transportation and to help continue to pay for the roads and bridges we will all continue to use. One place to start would be for Massachusetts to join with the other states in the Northeast to create a cap-and-invest program to cover transportation emissions. Funds from the sale of emissions allowances could be used to pay for charging stations, particularly for consumers who do not have garages, as well as other critical transportation needs, such as public transportation.

Other jurisdictions, including California, Ontario and Quebec have expanded the cap and invest model into transportation fuels and the result has been billions of dollars in new investments in clean transportation. In Massachusetts, a program similar to California's could unlock hundreds of millions of dollars in funding every year. Massachusetts should follow the example it helped create in RGGI and now build off the other transportation emissions programs beginning to spread across North America.

We cannot solve an economy-wide emissions problem by focusing almost entirely on electricity emissions, which now represent less than 20 percent of the total pollution in the state. We urge Massachusetts and other states in the Northeast to move forward with policies such as cap-and-invest that can put us on the path to clean transportation.Ken Kimmell is president, Union of Concerned Scientists and former commissioner of the Massachusetts Department of Environmental Protection. Dan Dolan is president of the New England Power Generators Association.